In recent years, a hierarchical virtual storage device has been known in which a library device provided with a low-cost recording medium having a large capacity such as a magnetic tape is used as a back end storage device (e.g., a secondary storage) and a storage device having a higher access speed such as a HDD (Hard Disk Drive) is used as a cache device (e.g., a primary storage). A virtual storage device is provided a control device which controls access to the cache device and the library device. The control device makes a host device to recognize that a logical volume stored in the cache device is a volume corresponding to a recording medium of the library device. Accordingly, the host device is able to use a large capacity storage area provided by the library device as if the storage area is connected to its own device.
Further, as an example of a technology regarding a storage device, a technology has been suggested in which a determination as to whether a virtual volume constituted by a plurality of virtual storage areas is regarded as a target to be a dynamical rearrangement is made depending on a condition based on an IOPS (Input Output Per Second). Further, a technology has also been known in which a storage area having a volume code is equally divided and a logical volume code is allowed to be associated with each of the divided sub-storage areas to retrieve the logical volume code associated with the volume code designated by a higher-level device.
Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2011-186794 and Japanese Laid-Open Patent Publication No. H09-50351.